The present invention relates in general to integrated circuits, and in particular to a circuit that provides two adjustable voltage regulators for systems having dual supply voltages.
The semiconductor industry continues to downsize device geometries with every new generation of devices. The smaller and higher density integrated circuit devices help reduce the cost of end products and facilitate manufacture of ever shrinking portable computing systems. A related and in some applications equally important performance consideration, is the power demands of a given device. Process and circuit designers continue to focus their efforts on developing circuits that take less silicon area and consume less power.
In the case of microprocessors, for example, previous generations were designed to operate with a single 5 volt power supply. For battery-operated portable applications where power consumption is more critical, microprocessors have been designed with core circuitry running at lower voltages of, for example, 3.3 volts while the interface circuitry runs at 5 volts. This power saving technique has been widely adopted in not only other (e.g., desktop) processor designs, but also in many other types of integrated circuits including memories and programmable logic. Accordingly, current generations of microprocessors are being designed with two power supplies, a first one at for example 3.3 volts, that powers the interface, and a second lower voltage at for example 2.8 volts that powers the core circuitry.
The requirement for two power supplies, however, poses a problem for the board designer. The silver box that supplies power to a processor mother-board typically provides only 5 and 12 volt power supply voltages. The output of the 5 volt power source must therefore be switched to generate two different voltages on the mother-board. This requires using voltage down converters that can generate lower voltages of for example 3.3 and 2.8 volts from the 5 volt source. This is further complicated by the fact that different microprocessors are designed to operate with different supply voltage levels. For example, the Intel P54 processor requires a 3.5 volt supply voltage, while the Intel P55C processor uses a dual supply arrangement with a 3.3 volt power supply for the interface and a 2.8 volt power supply for the core circuitry.
Furthermore, the electrical current requirements for two different supply voltages may differ substantially. The 3.3 volt supply, for example, provides power to the interface circuitry (I/Os) that typically runs at a lower frequency of, for example, approximately 60 to 70 MHz. The CPU core, on the other hand, is powered by the 2.8 volt supply that runs at frequencies ranging from, for example, 130 MHz to 200 MHz. These exemplary numbers roughly translate to electrical current requirements of about 1 to 3 Amperes for the 3.3 volt supply, versus 5 to 7 Amperes for the 2.8 volt supply. This demands different performance characteristics for a voltage regulator.
There is a need for an efficient and cost effective solution to providing voltage regulators for systems running with multiple different power supply voltages.